Hacking Information on the gamecard interface

[gegl]

Hello!

Does anybody know where to get information on the interface connecting the ds and the ROM (memory) in the game cards.

I think all Flashcard producers built this interface into a FPGA in their flashcards, but I don't think they will give away any info.
I saw the DS-Xtreme OpenSource Project but there's also no info about the interface.

thanks in advance for all help